Conventionally, various kinds of arts regarding to a GNSS receiver are devised. For example, in Patent Document 1, an art of, in a GNSS receiver, obtaining an ionospheric delay amount based on a plurality of wireless signals with frequencies different from each other, which are transmitted from the same satellite, is disclosed. Further, in Patent Document 2, an art of obtaining a pseudorange from which influence of an ionospheric delay is removed by using a method, so called an ionospheric free linear combination, is disclosed.